The invention relates to a circuit breaker comprising a removable calibrating unit comprising an external face.
Calibrating devices for circuit breakers are generally fitted on electronic trip devices. They essentially serve the purpose of limiting the rating of the circuit breaker to a value lower than or equal to the rated current. For example, for a circuit breaker whose rated current is 1000 A, the calibrating device can set the rating to 500, 600, 800 or 1000 A by means of removable units. If the 800 A unit is fitted on the trip device, the rating will then be 800 A, and the overload tripping threshold setting will be lower than or equal to 800A. To prevent assembly errors, an error prevention device prevents units being fitted which are not part of the series corresponding to the circuit breaker. An error prevention device of this kind is described in the Patent FR-A-2,583,569. The removable units comprise, in state-of-the-art manner, electronic components connected to pins. When the unit is fitted in the trip device, the pins are connected to connectors so as to connect the electronic components of the unit to circuits of the trip device. These components are generally resistors, memories or more complex logic circuits.
In addition to calibrating the maximum overload current, the units can serve the purpose of setting the parameters of other functions of the trip device, notably earth fault protection, instantaneous or short-circuit tripping current value, indication of tripping faults or implementation of additional functions. The calibrating units can also comprise means for adjusting the overload current threshold. In a state-of-the-art manner, these means are potentiometers or switches and resistors.
The removable units are generally fixed by screws. If these screws are metallic the insulation distances between the front panel of the circuit breaker or trip device and the electrical part are reduced. In the case where the screws are made of insulating material repeated operations progressively wear out the thread of the fixing means.